Swing adsorption processes are well known in the art for the separation of one or more gaseous components from a gas mixture. The term “swing adsorption process” includes all swing adsorption process including temperature swing adsorption (TSA), pressure swing adsorption (PSA), partial pressure swing adsorption (PPSA), rapid cycle pressure swing adsorption (RCPSA), rapid cycle thermal swing adsorption (RCTSA), rapid cycle partial pressure swing adsorption (RCPPSA), as well as combinations of these processes such as pressure/temperature swing adsorption.
The first step in any swing adsorption process cycle is an adsorption step. In the adsorption step a gaseous feed mixture is flowed through an adsorbent bed and one or more of the components of the gaseous feed mixture are adsorbed by the adsorbent. These adsorbed components are sometimes referred to as “strongly adsorbed” components”. The non-adsorbed components are sometimes referred to as the “weakly adsorbed” components and pass through the adsorbent bed, without being adsorbed, to form a product stream. Depending on feed composition, there can be several strongly adsorbed component fronts passing through the bed, but there is always one that leads. The gas ahead of the leading front has a composition near that of the product. Behind the leading front the gas has a composition with a significant concentration of at least one of the strongly adsorbed components. In a conventional swing adsorption process, the adsorption step is stopped well before the leading front breaks-through the end of the adsorbent bed. The amount of feed that emerges from the contactor before this step is halted determines, in part, product recovery and purity. Typically, the adsorption step is stopped when the front advances to no more than about 0.75 to 0.85 of the length of the adsorption bed, thus preventing the front from breaking through the adsorption bed. This leaves a significant amount of product from the adsorption step at the end of the bed at the beginning of the regeneration cycle. Design of the regeneration cycles typically attempts to capture as much of the product as possible, but a certain amount inevitably flows into the strongly adsorbed component product streams. In some instances, as much as a third of what would have been the product remains in the bed when the adsorption cycle is stopped. Therefore, there is a need in the swing adsorption art for processes that are able to mitigate the amount of product trapped at the end of the adsorption bed and improve utilization of the full capacity of the adsorbent material utilized.